1. Field of the Invention
The present invention relates to expanded thermoplastic resinous materials and a process for production thereof. More particularly, it is concerned with expanded thermoplastic resinous materials with excellent heat resistance, as obtained using styrene-based polymers having a mainly syndiotactic configuration, and a process for efficiently producing expanded materials from thermoplastic resins.
2. Description of the Related Art
Expanded materials obtained using styrene-based polymers having atactic configuration or olefin-based polymers such as polyethylene are well known. In particular, expanded materials obtained by using styrene-based polymers having the atactic configuration are widely used as expanded polystyrene or foamed polystyrene.
These expanded materials from polystyrene and polyethylene resins are unsatisfactory in heat resistance although those with low expansion ratio are used as construction materials, i.e., artificial wood and those with high expansion ratios are used as heat insulation materials. More particularly, expanded polystyrene is subject to thermal deformation when the temperature exceeds 100.degree. C. which is the glass transition temperature of atactic polystyrene. Also, expanded polyethylene is subject to thermal deformation when the temperature exceeds 135.degree. C.
Previous inventors have succeeded :n developing styrene-based polymers having high syndiotacticity and further provided compositions containing styrene-based polymers having high syndiotacticity. These results have been previously disclosed in Japanese Patent Application Laid-Open Nos. 104818/1987, 257948/1987 and 257950/1987.
These styrene-based polymers having syndiotactic configuration or compositions thereof are excellent in properties such as mechanical strength and heat resistance, as compared with styrene-based polymers having atactic configuration or their compositions.
Further investigations based on the above findings have shown that when styrene-based polymers having syndiotactic configuration or compositions thereof are expanded using a foaming agent, expanded materials which have much greater heat resistance than conventional expanded polystyrene resins, can be obtained.